Register correction for television



R. C. WEBB REGISTER CORRECTION FOR TELEVISION {June 27, 195o Filed July l, 1948 fw. J

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- IVENToR 423101743062 BY Q f ATTRNl-:Y

Patented June 27, 1950 UNITE STES REGISTER CORRECTION FOR" TELEVISION of Delaware Application July 1, 1948, Serial No. 36,395

1 Claim.

This invention relates to television systems and more particularly, but not necessarily exclusively, to correction of distortion which prevents accurate registration of component images when superposed.

In black and white television a certain amount of distortion Within the image raster can be tolerated or is unnoticeable, but when a plurality of rasters are superposed as is customary in simultaneous color television, the same degree of distortion becomes objectionable because the individual distortions seldom occur at corresponding parts of the image and the lack of registration becomes apparent. Camera tubes, such as the Orthicon and Image-Orthicon types and kthe coils associated therewith, are very carefully made and usually include shielding arrangements to insure uniform Ilux distribution and axially symmetric fringing ux in which the photocathode is located. Other types of tubes, wherein the scanning beam is angularly disposed to the target, produce a keystone eiect and various arrangements for correction thereof are known. However, in spite of all such precautions there are dissimilarities in tubes, electrodes, and connecting leads which cause unpredictable local distortions, especially near the edges of the image raster, Consequently, when two or more images are superposed, such local distortions are accentuated and become objectionable.

, The presence of such local distortions may also be objectionable in connection with a single tube, for instance, when a very accurate and undistorted image raster is desired.

The primary object of the present invention is to correct or compensate such local distortions.

A related object is to correct or compensate distortions in one or more of a plurality of television tubes so that the superposed images will register over the entire picture area.

Broadly, these objects are accomplished by disu posing a number of elements about that section of the tube where such elements can effect controllable modications in the iield of force Within the tube. For instance, with an Image- Orthicon tube such elements may be magnetic plugs disposed in the fringing flux of the focus coil, or they may be electrostatic elements disposed around the periphery of the image section of the tube. In any event the effect of each such element is made individually adjustable so that corrections can be applied to Various parts of the image without appreciably affecting other parts.

.A further object of the invention is to arrange the adjusting apparatus to be compact and quickly manipulated at a point Where the effects of the adjustments can readily be observed.

Other objects and advantages of the invention will be apparent from the following description of two embodiments thereof, in connection with the accompanying drawings, in which:

Figure 1 is an illustration of one embodiment of the invention using magnetic plugs as deflecting elements;

Figure 2 is an end view of Figure 1;

Figure 3 illustrates another embodiment using electrostatic elements;

Figure 4 is an end View of Figure 3 with modification;

Figure 5 shows control apparatus for three tubes according to FiguresI 3 and 4; and

Figure 6 shows circuit details for the apparatus of Figure 5.

Referring to Figure l, reference character I0 indicates a camera tube surrounded by a focus coil II. The end portion i2 of the camera tube is the image section thereof and is located near the end of coil II, the fringing ilux of which is indicated by dotted lines at i3. Disposed within such flux are a number of elements I4 of magnetic material, which may be supported in a non-magnetic ring I5 adjacent the ends of the image section I2 and coil II. Ihe magnetic elements Irl may have any one of various forms and may be supported in any suitable manner so long as they are adjustable toward and away from the flux I3. In the form shown, the elements are threaded plugs having depressions or slots I6 in one or both ends by which they can be screwed in or out of threaded holes in ring I5 and thereby adjusted individually relative to the flux I3. The plugs I4 may be of temporary magnetic material, such as soft iron, or they may be of permanent magnet material and `magnetized so that the ends of each plug are north and south poles respectively. In the latlter case the plugs should be made reversible end-to-end in the ring I5 so that either the north or the south pole of any plug can be presented to the fiux I3.

The operation of the arrangement shown in Figures 1 and 2 is as follows. rlhe tube I0 is put into operation so that it provides an electron stream representing an image in the image section I2 and the signals produced thereby are reproduced in any convenient manner. The plugs Ill may be symmetrically positioned with respect to the axis of tube I0. If any part of the raster shows distortion of the image, the

plug or plugs nearest to that part are adjusted toward or away from the fringing flux I3 until the distortion is corrected. Ordinarily three tubes such as Hi are used simultaneously, one for each of the colors, red, green, and blue. The three tubes are optically registered accurately but when the images are superposed, local electrical distortions become more evident due to the differences in color and the possibility that a distortion in one tube may be in the opposite direction from a, similar distortion in another tube. The plugs I4 of the ytube `0r"tubes vvhichy appear to be distorted, are lthenadjusted-for such part of the image rasterauntil an acceptable registration of all three colors is obtained. Soft iron plugs will concentrate the ux within themselves, the eiect thereof being'more pronounced as the plugs are moved toward the center of ring l5. If permanently magnetized plugs are used they will have a similar effect for one polarity, but will have the oppositeeffect, i. e. a dispersion of flux, when the plugs'are reversed end-to-end.

Figures .3 and 4 illustrate a second embodiment of the invention whereinelectrostaticelements vare used insteadpf :magnetic elements. 1nl this embodiment the image section l2 of tube ID is surrounded by a number of electrostatic members 23 which may be of any convenient f lit surrounds the members 20, the proportions being exaggerated for clearness. Each element or member-23 is connected `by a conducting lead 2| to an adjustable tap 22 on apotentiometer 23 Awhich preferably is Agrounded at its midpoint 24. Afsource-of D. C. potenti-alvmay--be connected Vto the yends of potentiometer 23 as indicated vby thev plus-and minus signs. .For convenience 'the taps22 in Figure 3 are shown in line-but it should be 4understood that they are 'arranged to pass reach other so rthat any'voltage available in potentiometer 23 may be applied to 'any one ofthe elements 20. Suchv an arrangement is illustrated vin Figure '4 lwherein the `potentiometer 23 is shown in lend view with the taps `22 'disposed :s

circumferentially.

Figures 5 and' 6 show another potentiometer arrangement wherein the adjusting apparatus 'for three camera tubes equipped withelements 2D (as shown kin Figures 3 and 4) isarranged on a panel 3B for convenience. Control knobs 3l, 32, and 33 of three potentiometers, 3b, y'and'l are Jai-ranged in a group and adjustable taps 38, "39, and 133 thereof `are connected respectively to corresponding elements 2l! of the three'tubes, as "indicated in Figure 6. For instance, .the element '26 shown at the 12 oclock position .(Figure' 4) of "tiometers -arefprovided on panel' for the respective electhe red tube is connected to tap 3B; the 12 oclock element of the green tube is connected to tap 39; and the 12 oclock element of the blue tube is connected to tap 4i). Thus the corresponding elements of the three tubes can be controlled by a group of closely adjacent poten- Additional groups of potentiometers trostatic elements and preferably are disposed -i'n a circle corresponding to the circle of elements 26 in vFigure 4.

'In Figure'the potentiometers 35, 36, and 31 vare connectedin parallel across a source of D. C. potential i32, the neutral point of which is grounded atll. The other groups of potentiomfeters may be similarly arranged and connected,

and source 43 may be common to all groups. The poten'tiometers may have high resistance so that all of them connected in parallel Will require little current.

The operation ofy the arrangements shownfin Figures 3 to 6, inclusive, is 'as follows. Thefrela.- tivev distortions of the three tubes aresnoted when all of the electrostatic elements 20 of all the tubes have the same potential, preferably neutral. Where'distortion is noticeable, the potentials of one or more of elements 20 of onefor more of the tubes are varied in either a-positive or a negative direction with respect to common ground untilthe distortions are correctedla'nd the three images are properly registered.

The apparatus described and the embodiments shown in the drawings are merely'illustrative, for it-'is obvious that substitutions and modifications can be made to suit particular requirements.

What is claimed is:

'An apparatus 'for correctingl 'and compensating for distortions in the inuencing eld vin the vicinity of a photocathode comprising radially disposed electrostatic Vmembers of conductive -material, said electrostatic 'members beingimounte'd externally with respect to the region of :the photocathode, and means for selectively yapplyingdifferent potentials to each of said electrostatic members.

i RICHARD C. *WEBB REFERENCES CITED The following references are of recordin'the le of this patent:

UNITED STATES PATENTS Number Name Date 1,985,093 Hehlgans Dec. 18, 1934 1,995,376 Campbell Mar. 26,1935 '2,004,099 Bedford June 11,:1935 2,157,182 Maloi May 9, .1939 2,165,803 'Maiori July 11, 1939 2,244,748 Walker vJune 1'0, 1941 2,258,643 Gier et al Oct. 14,1941 2,455,676 Hillier Dec. 7, 19548 

